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Bulky Ligand Systems Containing Pi-Acidic Aryl and Carboranyl Groups

Abstract

This thesis describes studies into the synthesis and coordination chemistry of ligands containing bulky π-acidic groups. Both π-acidic aryl and carboranyl groups have been investigated. Chapter One highlights electronic and structural aspects of ligands investigated and computational techniques employed. Chapter Two describes the synthesis of aromatic systems bearing nitrogen substituents and trifluoromethyl groups, with a view to their use in the synthesis of new ligands. The π -interaction between the nitrogen substituent and aromatic ring has been investigated and is found to vary considerably with the nature of the substituent and position of the CF(_3) groups on the ring. Chapter Three describes the synthesis of molybdenum compounds containing CF3 substituted aryl-imido ligands. The presence of the π-acidic group is found to decrease π-bonding from the ligand to the metal which results in changes in the reactivity of such complexes. Chapter Four describes the synthesis of nitrogen-substituted carboranes 1- NHX-2-R-l,2-C(_2)B (_10)H(_10) (R = Me, Ph; X = 2-R-l,2-C(_2)B(_10)H(_10), NHAr, OH, H) and 1- NX-2-R-C(_2)B(_10)H(_10) (R = Me, Ph; X = 0, NAr). The structures of many of these compounds are described and the π-interaction between the cage and substituent investigated. This 7t-interaction determines the orientation of the substituent relative to the cage and causes changes in the geometry of the cage. The "B NMR shift of the atom directly opposite the nitrogen substituent is found to give an accurate indication of the exo π-bond order. In light of these observations data from other systems have been re-examined. Chapter Five describes the incorporation of carborane containing ligands into metal systems. The π-acidic carboranyl group reduces 7i-bonding from the ligand to the metal. The consequences of this on the structure and reactivity of these complexes are discussed. Chapter Six gives experimental details for Chapters Two to Five. Richard John Peace (August 1996)